Distribution, uptake, and daily exposure of per- and polyfluoroalkyl substances in a paddy field: A growth cycle study

Abstract

Rice, a crucial agricultural commodity, is potentially susceptible to contamination by persistent organic pollutants throughout its entire growth cycle in the field. Per- and polyfluoroalkyl substances (PFASs) have attracted great scientific attention due to their environmental persistence, bioaccumulation potentials, and toxicity. However, the occurrence and behavior of PFASs in the paddy ecosystem have not been confirmed. This study explored the uptake, accumulation, and potential risks of PFASs in the irrigation water, soils and paddy tissues from a typical paddy system at the main stages of rice growth. The total PFAS concentrations in irrigation water and soils were in the range of 62.9−85.5 ng/L and 45.7−75.4 ng/g dw. The concentrations of PFASs in paddy tissues followed the order of root>stem>leaf>grain. A minor decrease in PFAS concentrations in paddy tissues with growth time may be attributed to biotransformation and growth dilution. PFAS distribution in soils, irrigation water, and different paddy tissues also showed different patterns with the growing time of paddy. ΣPFCAs and ΣPFSAs were the most prevalent PFASs in all samples, which constituted 65.0−96.3% of the total PFASs. In addition, the transfer factor (TF) values from root to stem/leaf/grain decreased as Log K_OW increased (Log K_OW< 5). Significant correlations between the concentrations and protein contents in paddy grains were observed for most long-chain PFASs. Risk assessments have suggested that the current levels do not pose a health risk to humans, but PFAS alternatives cannot be neglected for food safety and environmental impacts.

Environmental Implication

Concerns are mounting globally regarding the environmental implications of PFAS and human exposure through food consumption. This study elucidates the uptake and biotransformation of PFASs throughout paddy growth cycle. The findings reveal that PFASs can be taken up by roots and translocated to grains, suggesting potential pathway for these substances to enter the food chain. A positive correlation between translocation factors and protein content in paddy tissues. Further investigation is warranted on the emergence and behaviors of PFAS alternatives within the soil-plant system, as this is crucial for assessing the ultimate fate and potential toxicity of PFASs in the environment.